1. Field of the Invention
The present invention relates to a method and apparatus for a vehicle braking system. More particularly, the present invention relates to a method and apparatus for a vehicle braking system having at least one valve to provide a fluid pressure to a first directional transmission clutch rotating in a first direction to urge a second directional transmission clutch rotating in a direction opposite the first direction with a vehicle drivetrain to slow, or brake, the vehicle drivetrain.
2. Discussion of the Related Art
Engine braking control systems are well-known in the art. One such system has been described in U.S. Pat. No. 4,231,455. U.S. Pat. No. 4,231,455 depicts an air brake system to control the application of a separate and dedicated clutch brake and a transmission clutch simultaneously. More specifically, when braking is desired, the transmission controls act to engage one gear ratio establishing device for one ratio drive and the brake control engages the output brake and a second gear ratio establishing device for output and gear reaction braking. A brake piston acts on the brake clutch and the transmission clutch to put the planetary rings into kinematic lock.
In U.S. Pat. No. 5,105,923 an engine braking control system is provided which is capable of applying engine braking through the transmission as well as wheel braking. The system has shift solenoids which are activated to perform the down-shift operation by selectively engaging and disengaging frictional elements in a gear train. Sensors for monitoring vehicle speed, an opening angle of a throttle valve and the amount of depression of the brake pedal generating respective signals are included. The engine brake system receives each of the respective signals and compares them to predetermined stored values to control the down-shift operation.
The present invention has an advantage over the prior art by using the hydrodynamic transmission of the vehicle to absorb part of the braking energy thus reducing the size and cost of the service brakes for the vehicle. The present invention has a further advantage over the prior art of not requiring a separate brake clutch or a complicated downshift operation to slow, or brake, the vehicle.
The invention relates to a vehicle braking system having a brake system activation means for receiving a braking signal. At least one valve is connected to the brake system activation means for providing a fluid pressure through such as, for example, a pressurized transmission fluid, proportionally to the braking signal to a first directional transmission clutch rotating in a first direction. A second directional transmission clutch rotates in a second direction opposite the first direction with a vehicle drivetrain. Both the first and the second directional transmission clutches are connected to the vehicle drivetrain. The pressurized transmission fluid causes the first directional transmission clutch to urge the drivetrain to rotate in the first direction thus slowing, or braking, the drivetrain. A service brake system is connected to the vehicle brake system activation means to selectively engage at least one service brake.